1. Field of the Invention
The present invention relates to the use of rubber modified graft copolymers of acrylonitrile and methyl acrylate used as refrigerator liners. Such polymers comprising about 14 to 30 weight percent of a rubbery polymer and have excellent low temperature impact properties.
2. Description of the Prior Art
As used herein "refrigerator" shall mean any cabinet, room, chest, box or other container used to keep food or other items cool or frozen. Therefore, as used herein "refrigerator" includes within its scope, refrigerators, freezers and other similar appliances.
Currently refrigerator interiors (also referred to herein as liners or boxes and including within its scope racks, shelves, bins or other containers) are typically molded from acrylonitrile-butadiene-styrene resins (ABS) or high impact polystyrene (HIPS). ABS resins are generally superior in properties to HIPS resins for refrigerator liners but are somewhat more expensive. The liners are encased by a metal outer shell and between the liner and outer shell, insulation is added to decrease the heat transfer into the refrigerator box.
In the past, the insulation was blown into the cavity between the inner box and outer shell using chlorofluorocarbon (CFC) blowing agents. For environmental reasons, such blowing agents are being replaced by hydrochlorofluorocarbon (HCFC) blowing agents. Unfortunately, HCFC blowing agents attack and degrade the current HIPS or ABS liners causing the liners to lose impact strength and become more susceptable to breaking or cracking during normal use.
Rubber modified graft polymers of acrylonitrile and methyl acrylate as described in U.S. Pat. No. 3,426,102 are known for good impact resistance as well as good chemical and solvent resistance. However, commercial grades of such copolymers typically had a lower impact strength than ABS at normal refrigeration temperatures and were not believed to be suitable for such applications.
An object of the instant invention is to develop a refrigerator liner made from a moldable resin having excellent impact properties at low temperatures, which would not be attacked or degraded by the HCFC blowing agents used in conjunction with the insulation materials used in refrigerators.